In view of improvements in the visibility of liquid crystal displays, conventionally, techniques for efficiently introducing light from light sources to liquid crystal displays or the like generally employ light-condensing elements having a specific surface shape, such as prism sheets and lens array sheets, to condense outgoing light into the front direction and to increase the brightness.
However, such light-condensing elements having a specific surface shape have to be placed via an air layer, because, in principle, the condensation of light with such elements needs a relatively large difference in refractive index. Thus, the conventional techniques have problems such as an increase in the number of parts, light loss due to unnecessary scattering, surface damages, and visible contamination of the installed clearance with foreign matters.
A lighting system including a reflecting layer provided on the lower surface of a light guide plate and a reflection polarizer provided on the light-emitting side is also proposed for improvements of techniques in the brightness of emitting polarized light. As used herein, the term “reflection polarizer” means an element having the function of separating components of incident natural light into transmitted polarized light and reflected polarized light depending on the state of polarization.
It is disclosed that if a retardation plate that is controlled so as to have specifically different retardations with respect to vertical incident light and obliquely incident light is placed between polarizers, the angle distribution of transmitted lights can be restricted, and lights in or near the front direction can only be transmitted and other outside lights can be entirely absorbed when an absorption polarizer is used (for example, see Japanese Patent No. 2561483 and Japanese Patent Application Laid-Open (JP-A) No. 10-321025). If a reflection polarizer is used in place of the absorption polarizer, lights in or near the front direction can only be transmitted and other outside lights can be entirely reflected. According to this theory, lights emitted from a backlight can be condensed or collimated with no absorption loss.
A light-condensing system using such a reflection polarizer can be tens to hundreds μm in thickness even if the collimating layer of a thin film includes the reflection polarizer. Thus, such a system can be easily designed to be very thin relative to prism array or lens array sheets. Such the system needs no air interface and thus can be pasted for use. Thus, such the system is advantageous in handling terms. For example, if a cholesteric liquid crystal polymer (about 10 μm in thickness) is used as the reflection polarizer in combination with a thin coating film of a liquid crystal polymer (about 5 μm in thickness) serving as a retardation plate, which is laminated with an adhesive layer (about 5 μm in thickness), the total thickness of the resulting system can be as thin as 50 μm or less. If the respective layers are directly applied so as not to produce interfaces, the resulting system can be thinner.